Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

The Pliocene‐Quaternary wedge‐top basins of southern Italy: an expression of propagating lateral slab tear beneath the Apennines

Abstract: In recent years, contrasting seismic tomographic images have given rise to an extensive debate about the occurrence and implications of migrating slab detachment beneath southern Italy. One of the most pertinent aspects of this process is the concentration of the slab pull force, and particularly its surface expression in terms of vertical motions and related basin subsidence/uplift. In this study we focused on shallow-water to continental, Pliocene-Quaternary basins that formed on top of the Apennine allochthonous wedge after its emplacement onto a large foreland carbonate platform domain (Apulian Platform). Due to the thick-skinned style of deformation controlling the Pliocene-Pleistocene stages of continental shortening, a high degree of coupling with the downgoing plate appears to characterize the late tectonic evolution of the southern Apennines. Therefore, the wedgetop basins analysed in this study, although occurring on the deformed edge of the overriding plate, are capable of recording deep geodynamic processes affecting the slab. Detailed stratigraphic work on these wedge-top basins points to a progressive SE-ward migration of basin subsidence from c. 4 to c. 2.8 Ma over a distance of about 140 km along the strike of the Apennine belt. Such a migration is consistent with a redistribution of slab-pull forces associated with the progressive lateral migration at a mean rate in the range of 12–14 cm y–1 of a slab tear within the down-going Adriatic lithosphere. These results yield fundamental information on the rates of first-order geodynamic processes affecting the slab, and on related surface response.

Behavior of Composite Timber‐Concrete Floors

Abstract: Timber‐concrete floors are widely used in the Persian Gulf region because of their resistance to the hot and aggressive environment of the area Because no shear connector is provided, the timber joists and concrete slab work independently In this study, it is suggested that relatively inexpensive high‐strength nails be used as shear connectors so that the timber joists and concrete slab resist the loads as a composite section Experimental investigations have shown that it is possible to attain full composite action through the use of these high‐strength nails The proposed composite timber‐concrete floor system was subjected to static short‐term loading, repeated loading, and long‐term sustained loading It is observed that in terms of strength and serviceability the behavior of the proposed system is within the limits set by standard building code This behavior is also verified by a finite‐element analysis The experimental and numerical results clearly reveal that it is possible to achieve a stiffer

Detailed look at final stage of plate break‐off is target of study in Romania

Abstract: Geophysical experiments next year in Romania may provide insight into a common but short-lived seismic process that can be observed and understood at only one spot on Earth at present. About 150 stations will be set up in the Vrancea area in the southeast Carpathian Mountains to, in effect, record the terminal phase of the detachment of a subducting slab of oceanic lithosphere. This is a major regional tomographic study using a large number of broadband seismometers, which will operate for 6 months. Images will be used for hazard assessment as well as for a delineation of detachment history. Active subduction of oceanic lithosphere at convergent plate boundaries involves earthquakes, magmatism, metamorphism, and deformation—some of the most vivid manifestations of any plate tectonic process. The initiation and termination of subduction, however, remains relatively poorly understood. When convergence of lithospheric plates ceases and the suction force of the subducting plate becomes negligible, the subducting slab moves into an almost vertical position. If subduction occurs in an arcuate geometry, the slab is likely to be segmented.

Dispersion of P waves in subducted lithosphere: Evidence for an eclogite layer

Abstract: Cold, subducted lithosphere has relatively fast seismic velocity which leads to early arrivals for some event-station paths. The effect is very large for events in the Tonga-Kermadec deep seismic zone recorded at certain New Zealand stations. These particular arrivals are very high-frequency (3 Hz or greater) and sometimes resemble two distinct phases, the later arrival appearing at about the time predicted by Jeffreys-Bullen tables. Data from the digital station SNZO in Wellington confirm the travel time results of the analog stations and furthermore show frequencies above 5 Hz, much higher than can be seen on analog records, and up to 4% dispersion in the range 1–8 Hz. Energy in the second phase (which is often absent at SNZO) is mainly 1–2 Hz. The digital data support the idea, proposed earlier, that the effect is caused by propagation through a thin slab which passes only short-wavelength waves. The essential features of the wave propagation are modeled by acoustic waves in a one-dimensional high-velocity slab; the waveforms produced by the model are discussed in terms of the leaky modes of the system and calculated by a reflectivity method. A very thin (< 15 km) uniform slab provides the required dispersion, but the waves are heavily attenuated and would never be observed at teleseismic distances; a thicker slab allows the energy through but does not give enough dispersion. Altering the variation of velocity across the slab provides the required dispersion if a thick high-velocity layer, with wave speed increasing gradually with height, is overlain by a thin lid of even higher velocity. For the models considered the lid thickness must lie in the range 6–15 km and be continuous from a depth of about 50 km to the bottom of the earthquake zone. The thick layer could arise from the thermal anomaly in the subducted lithosphere; the thin lid may be the gabbroic part of the subducted crust that has transformed to eclogite.